Oven-thermometer.



C. D. BOLIN.

OVEN THERMOMETER.

APPLICATION FILED JULY 6. 19:5.

Patented May 8, 1917.

CHARLES n. BOLIN, or s'r. LOUIS, MISSOURI.

OVEN-THERMOMETER.

Specification of Letters Patent.

Patented May 8, 1917.

Application filed July 6, 1915. Serial No. 38,080.

construction and arrangement of the spring and indicating mechanism for showing the amount of distortion of the spring and the corresponding temperature. 7

The object of the invention is to reduce the number of parts, and to cheapen the cost of manufacture, of such thermometers by simplifying the construction of the operating parts. Further details of the invention appear in the following description of the oven thermometer illustrated in the accompanying drawings, and what the invention consists in is more particularly defined in the appended claims.

In the drawings, in which like parts are designated by the same reference characters in the several views,

Figure 1 is a. front view of an oven thermometer made in accordance with this invention;

Fig. 2 is a front view of the same with the front glass and dial removed, and index pointer broken ed to show the parts within the inner chamber of the case;

Fig. 3 is a vertical cross section of the same on the line 3-8 in Fig. 1; and

the bi-metallic heat sensitive spring, indexpointer, and index-pointer pivot, respectively.

Referring to the drawings, the improved device comprises a cylindrical casing 11, having a back wall 12 which forms a support for the heat sensitive spring 13 and indicating mechanism. The back wall 12 has two diametrically opposed ears or lugs 14 provided with slots 15 through which may be passed bolts or screws for securing the device to the door of an oven. The cylindrical casing 11 projects through the oven door, and a face or dial 16 covers its open front side. Over the dial is a glass 17, held by an outer casing ring 18 which surrounds the casing 11 and which has an inturned lip or flange 19 inclosing the glass. A separator ring 20 within the casing ring 18 between the glass and the dial holds the glass spaced away from the dial and in contact with the flange 19, as shown in Fig. 3.

The heat sensitive spring 13 is fiat, and is riveted at one end to the side of a post 28 which is secured to the back wall 12 of the casing. The other end of the spring 13 carries a finger or pin 24 which is fixedly secured to the spring 011 one side and which pro ects outwardly beyondthe edge of the spring toward the dial to engage the slot in the arm 25 on the inner end of the index pointer.

The heat sensitive spring is composed of two co-extensive leaves 21, 22, secured together fiatwise, these leaves being made of metals having different coefficients of expansion, such as nickel steel and brass. The effect of changes in temperature is to bend or bow the spring sidewise, thereby causing the pin to swing the slotted arm 25 and de flect the index pointer.

The dial 16 is marked with a scale 27 reading from about 100 to about 500 degrees "and extends through the dial, forming an integral connection betweenthe hand 26 and V the inner slotted arm 25. The hand 26, con- Figs. 4, 5 and 6 are perspective views of p necting, portion 29 and inner slotted arm 25 of the index pointer are all made in one piece by stamping them from sheet metal, and are then bent into the form shown in Fig. 5. The connecting portion 29 can be easy to assemble. The heat sensitive spring is straight at ordinary room temperature, and consequently. requires no bending or other adjustment, the relative positions of the slotted arm and pointer being adjustable to suit small variations in the setting of the spring. There are only two moving parts, which reduces the lost motion and backlash of the connections and pivots to a minimum, and hence increases the accuracy and life of the instrument. Furthermore, the casing being completely closed on the back or oven side, no dirt, grease or smoke from the oven can get into it to gum up or corrode the moving parts, and therefore the device will not become sluggish or inaccurate in the course of a comparatively short time, as might be the case if it were not so protected.

The invention is not limited to the precise forms and arrangement of the parts shown and described.

I claim the following as my invention:

1. A thermometer comprising a casing and a heat sensitive spring inclosed therein and fixed thereto at one end, said spring having a finger at its free end, a pivot post fixed to the casing at its inner end and projecting out of the casing and carrying an index pointer pivoted on its outer end, said index pointer having an inner portion provided with an arm pivotally engaging said post within the casing, said arm having an opening in which said finger is engaged for turning the pointer on its pivot.

2. A thermometer comprising a casing with an open front closed by a dial and a heat sensitive spring inclosed in said casing and fixed to its back wall at one end, said spring having a finger at its free end, a pivot post fixed to the back wall of the easing at its inner end and projecting through said dial and carrying an index pointer pivoted on its outer end to sweep across the face of said dial, said index pointer having an inner portion provided with an arm within the casing, said arm having an opening in which said finger is engaged for turning the pointer on its pivot.

3. A thermometer comprising a support and a heat sensitive element fixed thereto, a dial, and a sheet metal index pointer swinging across said dial, said pointer having a hand and an arm in parallel planes on opposite sides of said dial, a pivot fixed to said support and passing through said dial and said pointer, and a strap passing through said dial alongside of said pivot and connecting Said hand and arm, whereby said hand and said arm are caused to swing in unison, and means connecting said arm and heat sensitive element for swinging said arm in response to deflection of said heat sensitive element.

4. A thermometer comprising a base and a heat sensitive element fixed thereto, a dial, and a sheet metal index pointer swinging across said dial, said pointer having a hand and an arm in parallel planes, a pivot fixed to said base and passing through said hand and said arm, and a strap alongside of said pivot connecting said hand and arm and long enough to be twisted between its ends without injury, whereby said hand and said arm can be adjusted to stand at any desired angle to each other and are caused to swing in unison, and means connecting said arm and heat sensitive element for swinging said arm in response to deflection of said heat sensitive element.

,5. As an article ofmanufacture, a thermometer needle formed from a. single piece of sheet metal having two parallelly arranged arms, one disposed above the other, one arm serving as a heat indicating memher and the other arm having provision for connection with a heat responsive member, a yoke formed integral with the arms for rigidly connecting them, there being a pivot hole in each arm, the pivot holes being in registration with each other.

Signed at St. Louis, Missouri, this 30th day of June, 1915.

CHAS. D. BOLIN.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, 1,). G 

